Cerebral Intracellular ADP Concentrations during Hypercarbia: An in vivo 31 P Nuclear Magnetic Resonance Study in Rats

Qualitatively different responses of ADP levels have previously been observed in the brain during hypercarbia. One investigation has found that cerebral ADP stayed constant during hypercarbia in rats that were anesthetized with halothane, while another observed that ADP decreased during supercarbia in rats that received no supplemental anesthesia. This article reports an in vivo 31P nuclear magnetic resonance study to test the hypothesis that halothane anesthesia accounts for the discrepant observations. Isoflurane anesthesia was also studied in a second group of rats to see if a different general anesthetic agent would cause the same effects that halothane causes. The two groups of five rats underwent dual episodes of hypercarbia that were separated by a 45-min recovery period. General anesthesia, either 0.5% halothane or 1.0% isoflurane, was administered during the first episode but not during the second. Hypercarbia during halothane anesthesia caused the measured phosphocreatine (PCr) to decrease by 40%, while the calculated change in ADP was 10%, in agreement with the former investigation. In contrast, hypercarbia during either isoflurane anesthesia or no anesthesia caused a decrease of only 10% in PCr, which meant that the calculated decrease in ADP was 60%, in agreement with the results of the second investigation. We conclude that during hypercarbia, clinical concentrations of halothane, unlike clinical concentrations of isoflurane, interfere with the regulation of ATP metabolism.